In conventional systems process for developing passive suspensions involve vehicle modelling and simulation to vary parameter values to achieve an acceptable compromise between competing vehicle attributes such as ride and handling within a given suspension working space. Controllable suspension elements (such as switchable dampers, controlled roll bars and variable spring elements) have been introduced to maintain the lateral force generating capability of the tyre contact patch. This is achieved by control of wheel camber, steer angle and normal loading and, generally speaking, controllable suspension elements are compatible with all systems which vary applied wheel torque since the systems are complementary. In a similar way, systems contributing to wheel torque (engine, transmission, active drive line) have been developed. However in many conventional systems the different elements are controlled by distributed autonomous controllers giving rise to significant conflicts.
In one known system a supervisor assesses driver demand from inputs such as steering wheel and accelerator pedal and provides a vehicle output in the form of speed, torque and so forth based on safety considerations. This approach has various limitations. First of all if the driver increases demand beyond a limit then no additional response is seen. Furthermore the driver is not provided with feedback as to the effect of the inputs he is providing and whether he is approaching a limit condition. As a result driver demand may not be met, or the driver may not be able to detect this which is unsatisfactory to the driver. Yet further known systems are not able to fully determine the current vehicle state including parameters that significantly affect performance and safety, such as vehicle slip angle, further degrading their performance.
A further problem with known systems is that different driver inputs for example steering and accelerator pedal may present conflicting messages. This can especially be the case where an inexperienced driver, in an attempt to signal demand, controls the vehicle inexpertly during a difficult manoeuvre (for example backing out during a limit handling manoeuvre) or indeed a very experienced driver carries out highly skilled manoeuvres such as applying an “opposite lock” during a manoeuvre. Such conflicting signals can be misread by existing systems giving rise to significant performance and safety concerns.
Yet a further problem with known systems in encountered in the existing control hierarchy model. Known systems include a supervisor and sub-systems comprising multiple actuators such as brake, chassis, suspension, torque differential controllers. In these known systems the actuators can carry local sensors to detect a current operating condition. As a result when the supervisor sends a command to the actuator the actuator may override the command as a result of the current operating conditions. This is especially a problem in the automobile sector where many of the sub-system actuators are proprietary to different manufacturers such that conflict can often arise. As a result the performance of the vehicle as a whole is compromised because the supervisor does not have fully integrated control. Yet further the supervisor in conventional systems simply sends out set points to be met by each actuator which is inflexible, requires constant update and may also provide risk of failure modes.
The invention is set out in the appended claims.